The OpenBeam Kossel family of 3D Printers belong to a class of printers known as "Deltabots". Developed at Metrix Create:Space in conjunction with Johann Rocholl, the father of deltabots, Matthew Wilson, the creator of the original Brainwave 3D Printer controller board, and Mike Ziomkowski of Z-Designs USA, the designer of the Brainwave Pro. The original design goal was to create an alternate to the typical Reprap style cartesian robots and being able to circumvent some of Makerbot / Stratasys's intellectual property protection in the area.
In a deltabot style printer, linear motion in X, Y and Z are achieved by mixing input from 3 vertical, stepper driven towers. A series of ball joints link to an end effector platform onto which the hot end is mounted. From a mechanical assembly standpoint, the machine is easier to build; the user simply builds the same vertical tower subassembly three times. It also eliminates the need for lead screws for the Z-axis and allows equally fast motion in Z-Axis as well as X and Y.
From a legal standpoint, Stratasys's patent specifically claims a Cartesian XY Gantry system in a heated build chamber (see Claim 1 on the linked patent). The heated build chamber is important because it allows prints to cool uniformly after the print is done to relief any stress that are built up in the part that will eventually lead to warped parts. By using a Delta-style geometry, we can build a printer with an enclosed build chamber without violating the claims laid out in the Stratasys patent.
Ball joints are used to link the three towers to an end effector. The extruder cold end extruder and extruder motor is intentionally kept off the end effector to minimize the moving mass. This, coupled with the nature of belt drives, means that the printer can move extremely fast, and it can also move in Z as fast as it can in X and Y.
One unique feature that arises from this is the inclusion of an automated bed levelling probe. Ask any veteran 3D Printer operator and they will tell you that one of the more challenging aspects of 3D Printing is getting a good first layer adhesion.
On the Kossel family of printers at the start of each print, a touch probe is deployed and probes the bed surface. The drive firmware then takes these measurements and generate a 7x7 matrix of coordinates to offset each layer printed, thus allowing perfect adhesion and correcting for any calibration issues.
We used linear motion components that are slightly better than what is found in most Reprap machines. Our linear rails are cheap Chinese copies of the same rails used in optical instruments. They are not as smooth, but they add tremendous amount of rigidity to the machine chassis and does not adversely affect printer performance. Take a look at the gallery of prints made on Kossel machines and see for youself.
OpenBeam completed a successful Kickstarter for the Kossel Pro - a souped up version of the Kossel with mass produced parts, to further drive up the machine quality. The work is still in progress - feel free to follow our progress on the OpenBeam blog or search through our old blog articles via the tag cloud below: